Various injection devices exist that use a form of an automated mechanism to actuate injection of a liquid medicament into a patient. Examples of such devices include jet injectors, both needle-free and needle-assisted, and autoinjectors. Although the precise mechanisms used to complete injection can vary within and between these devices, most include a feature within the injection mechanism that stores kinetic energy to be used to drive the injection mechanism during use. Further, many known injection mechanisms include a trigger mechanism to secure the device such that the kinetic energy remains stored until injection is desired, whereby actuation of the trigger releases the injection mechanism, allowing the stored kinetic energy drives the injection mechanism to cause injection.
Examples of needle-free jet injectors are described in U.S. Pat. Nos. 5,599,302; 5,062,830; and 4,790,824. These traditional injectors administer medication as a fine, high velocity jet delivered under sufficient pressure to enable the jet to pass through the skin. The pressure used to deliver the medication is typically greater than approximately 4000 p.s.i. inside the compartment that contains the medicament in the injector. The injection mechanism in such needle-free jet injectors can be arranged to apply a force to a medicament storing chamber within the device such that the required pressure is created within the chamber.
Self-injectors or autoinjectors like the ones disclosed in U.S. Pat. Nos. 4,553,962 and 4,378,015 and PCT Publications WO 95/29720 and WO 97/14455 are constructed to inject medicament at a rate and in a manner similar to hand-operated hypodermic syringes. The self-injectors or autoinjectors have needles that are extended at the time of activation to penetrate the user's skin to deliver medicament through movement of the drug container and related needle. Thus the mechanism that provides the force to deliver the medicament in self-injectors and autoinjectors is also used to extend the needle and the drug container to cause the insertion of the needle through the user's skin and then to apply a force to a plunger movably disposed within the drug container to cause the medicament to be expelled from the container through the needle. The autoinjectors manufactured, for example by Owen Mumford, thus use very low pressures to inject the medicament, which is injected through a needle in a relatively slow stream. The pressures applied in the medicament-containing compartments of this type of device are very low, reaching a maximum of around 60 p.s.i. and take around 5 to 10 seconds to inject 1 mL.
Additionally, needle-assisted jet injectors have been developed that utilize a needle to initially penetrate the skin, most often to a depth less than that of a traditional hypodermic injector or autoinjectors. Once the skin is penetrated with the needle, the jet mechanism is activated, causing the medicament containing liquid within the injector to be pressurized and expelled through the needle and into the skin. The injection mechanism in needle-assisted jet injectors can be configured to move the drug container and the needle to move forward to penetrate the skin and then exert the necessary injection force to a plunger moveably disposed within the container. Alternatively, the needle and drug container can be properly positioned to penetrate the skin by bringing said needle and container to close proximity with the skin resulting in needle insertion while keeping the needle and drug container in a stationary position and the injection mechanism can be structured to pressurize the container. The pressure of the medicament within the injector can be less than that of a traditional jet injector, because the tough outer layers of the skin have already been penetrated by the needle. Similarly, the pressure of the medicament is preferably higher than that of an auto injector or the like, causing the medicament to penetrate the skin or the tissue below the skin to a depth that is sufficient so that with the needle penetration and penetration the medicament remains substantially within the body. An additional benefit of the higher pressure exists in a faster time of injection resulting in less psychological trauma to the patient and decreasing the likelihood of the user inadvertently terminating the injection prematurely by removing the injector from the injection site.
Because of the stored kinetic energy associated with the trigger and injection mechanisms, accidental firing can occur due to sudden movements during shipping or due to mishandling of the device by a user including accidental actuation of the trigger mechanism. Accidental firing of the injection mechanism can cause the medicament to be expelled from the device, which can be at a dangerously high pressure, depending on the type of injection device. Further, accidental firing can cause an injection needle to move forward with respect to the device with sufficient force to penetrate the skin.
An injector is needed that provides a reduced risk of accidental firing during shipping or handling thereof.
Additionally, many such injection devices are intended to be used a single time only. Accordingly, a locking mechanism is desired that prevents unintended repeated use thereof.